1. Field of the Invention
The present invention is directed to an ultrasonic stir welding device and method, and more particularly, to a method and device for welding utilizing ultrasonic frequency to provide heat to at least assist in plasticizing a work piece with a stir welding process.
2. Description of Related Art
The general concept of friction stir welding is described in U.S. Pat. No. 5,460,317. Conventional friction stir welding is a process of welding component parts together using frictional heat generated by a non-consumable tool to join work piece sections. The tool includes a pin that is inserted into the joint and a shoulder that is urged against an upper surface of the work piece. The pin and shoulder rotate dependently or as a single entity to generate friction needed to create a plasticized region along the joint for the welding operation.
In the traditional friction stir welding process, a pin tool consisting of a rotating shoulder, rotating pin and high forces are utilized to join material together. The rotating shoulder, in combination with high forces, produces much of the heat utilized to bring the materials into the plastic state. Having the materials in the plastic state is a requirement for successful solid state joining. Normally, the conventional friction stir welding process requires expensive reactive tooling and fixturing. Also, since the shoulder is coupled to the pin in the known friction stir welding technology, (1) the rpm of the pin tool controls the performance of the coupled pin tool and shoulder as well as (2) the pressure of the shoulder against the workpiece are key variables which affect welding performance.
Accordingly, there exists a need for a tool and method for performing stir welding which need not rely primarily on a single unique rpm or rate of revolution to control the coupled stir pin and shoulder, shoulder pressure and heat input.